n, m = map(int, input().split())
board = [list(map(int, input().split())) for _ in range(n)]
dp = [[0 for _ in range(m + 1)] for _ in range(n + 1)]
ans = 0
for i in range(1, n + 1):
    for j in range(1, m + 1):
        if board[i - 1][j - 1]:
            dp[i][j] = min(dp[i - 1][j], dp[i][j - 1], dp[i - 1][j - 1]) + 1
        ans = max(ans, dp[i][j])
print(ans)
